With the recent growth in the use of the Internet and expansion of small and home offices, there has been a great demand for high speed data services at numerous premises. Many phone companies have responded to this demand by offering DSL (Digital Subscriber Line) services over their existing telephone lines. Another popular broadband network uses the cable TV (Television) network.
DSL services allow information to be transmitted over the phone line in digital form. With the digital encoding used in a DSL system, the number of bits that can be transmitted through a phone line is much greater than with a traditional analog modem.
One form of DSL service is an Asymmetric DSL (ADSL) service. With ADSL service, the downstream data flow rate is greater than upstream data flow rate. Conventionally, for ADSL1, the band from 25.875 kHz to 138 kHz is used for upstream communications, while the band from 138 kHz to 1104 kHz is used for downstream communication. Other forms of DSL networks include ADSL2, ADSL2plus, VDSL1 and VDSL2, generically xDSL, which typically operate at different frequency bands.
In these broadband networks, individual subscribers are generally connected to the network through the telephone access network. In an ADSL network, the access network is usually physically implemented on twisted pair copper wires originally deployed for narrowband voice telephony. These wires are routed from a central office in cable bundles that each runs through a neighborhood or other portion of the service area for the network. Wires are branched from the cable to make connection to individual homes or offices in the service area. A device at the central office is connected to the rest of the broadband network and can route signals from the network onto a particular subscriber line. In an ADSL network, the exchange device is called a Digital Subscriber Line Access Multiplexer (DSLAM).
A cable TV network is conceptually similar, though implemented with different hardware. The broadband cable TV network includes many access networks through which subscribers are connected to the network. Subscribers in a particular neighborhood are connected through a common cable to a neighborhood router. Information on a cable network is transmitted using IP addressing, with each subscriber having its own IP address. In this way, each subscriber receives information directed to it as part of a “virtual” subscriber line.
The access portion of a network has traditionally been one of the most difficult parts of the network for a service provider to maintain. A network service provider might provide service to hundreds of thousands of subscribers. Clusters of subscribers will access the network through different access networks. Thus, there are many access networks that must be maintained. Further, the access networks are physically spread out over a wide area, exposing the access networks to significant potential for fault or interference. Furthermore, the geographical dispersion of the access networks also makes it expensive and difficult to identify and locate conditions that might affect service to users of the network.
Herein, a DSL network, more specifically an ADSL network, will be used as an example of a broadband network. However, cable and other types of broadband networks exist and experience problems analogous to those encountered in DSL networks.
Certain telephone line impairments at or near the customer premises require field technicians to be dispatched to the customer premises to make tests to uncover the impairments. Some of these impairments include making accurate measurements of line length and insertion loss, a far end series resistance fault, double ended balance of the line and whether adjacent circuits at the customer premises are radiating noise into the cable which can affect the service of the line.
For example, it is desirable for wires in the line to be balanced. In a balanced line, the resistance, capacitance and inductance of each wire are equal. Imbalances exist if capacitance, inductance or resistance of one of the wires differs from the other. A single ended balance test can be performed at the central office. This is done by transmitting a signal from the central office and making measurements at the central office, i.e., at the near end. However not all fault conditions will be observable from the central office. To perform a double ended balance test, and detect all line impairments, a technician must be present at the customer's premises, i.e. at the far end, to send a required signal to the near end and/or measure a signal from the near end.
It would be desirable and cost affective for a network operator to be able to quickly identify such “far end” service affecting conditions, without dispatching a technician.
The present invention is intended to allow exchange based measurements to identify the presence of telephone line impairments at or near the customer premises which cannot normally be detected from the exchange.